Heating, Ventilating, and Cooling
Your heating system simply heats up air or water, and then moves that heated air or water (or steam) around the house. It's really that simple. However, the technology behind this process is pretty complicated, which means that a professional must perform most maintenance tasks associated with it.
Window units which also can be installed through the wall, are refrigeration-type air conditioners. Central systems typically are refrigeration units too, but in hot/dry areas, evaporation units (sometimes informally called "swamp coolers") are popular.
When we talk about ventilation, we actually are talking about both interior ventilation and structural ventilation. Interior ventilation helps your home rid itself of moisture, smoke, cooking odors, and indoor pollutants. Structural ventilation controls heat levels in the attic and moderates dampness in the crawlspace and basement.